In late years, as the spread of IC cards, portable communications equipment and the like, or miniaturization and thinning of electronic equipment have been in high demand, the thinning of a semiconductor chip has been further required. Conventionally, a thickness of a semiconductor chip was approximately 300 μm. However, the thinning of 150 μm or less has been required depending on its usage.
A semiconductor chip is generally manufactured through a step of adhering an adhesive film for protection of a semiconductor wafer to a surface of a semiconductor wafer on which an integrated circuit is formed, a step of thinning by processing a back side of a semiconductor wafer, a step of peeling the adhesive film for protection of the semiconductor wafer and a step of dicing the semiconductor wafer. Especially, when the thickness is removed to as low as 150 μm, the thickness is first thinned to approximately from 200 μm to 150 μm by means of a step of conventional grinding processing, and sometimes a grinding processing, a chemical etching processing and the like may be subsequently performed for further thinning.
However, such a thinned semiconductor wafer may tend to have a significant degree of warpage deformation due to deterioration of its rigidity, which becomes a manufacturing problem. Usually in a step of thinning a semiconductor chip, every piece of a semiconductor wafer is taken out of a wafer case by a robot and fixed to a jig which is called a chuck table in the processing machine to carry out a back side processing. The wafer after the back side processing is carried back into the wafer case by a robot or conveyed to the next step. If warpage in the wafer becomes significant during these steps, some of the steps may come to a halt because the wafer is broken or the robot can not convey the wafer and the like. Also, in a step of peeling an adhesive film for protection of a semiconductor wafer, serious problems such as breakage of wafers may occur because wafers are planarized by force in fixing the wafer to the chuck table in the peeling machine.
Such warpage is considered to occur by the residual stress of an adhesive film for protection of a semiconductor wafer which is adhered on the surface of a wafer and residual stress of an integrated circuit protection film which is mounted on the wafer surface. The residual stress of an adhesive film for protection of a semiconductor wafer occurs by tensile force which is applied to the adhesive film when it is adhered to the surface of the semiconductor wafer. Generally speaking, an adhesive film for protection of a semiconductor wafer using a flexible base film which is easily stretchable tends to cause big residual stresses, resulting in easily causing warpage in semiconductor wafers.
On the other hand, the residual stress applied to the circuit protection film is remarkable in the case of polyimide group protection films. Especially, if the polyimide group protection film is thick, warpage in the wafer increases by the residual stress of the polyimide group protecting film in thinning a semiconductor wafer. As a result, serious problems such as a halt of steps occur because wafers are broken or the robot can not convey the wafer and the like.